Cathode ray tube



April 28 1970 sATosHl SHIMADA 3,509,416

GATHODE RAY TUBE Filed Dec. 25. 1966 2 Shees-Sheet 1 @eros/w SM1/MDA i E. BY

April 28, 1970 sATosHl SHIMADA 3,509,416

CATHODE RAY TUBE Filed Deo. 2:5, 196e a sheets-sheet 2 INVENTOR.

aros/x/ 6MM/9m, BY

A Trae/Vey l United States Patent O U.S. Cl. 315-21 3 Claims ABSTRACT F THE DISCLOSURE This invention relates to a single gun type post-acceleration and focusing tube with an improved color switching device including two pairs of outer electrodes provided on opposite outer surfaces of the neck portion of the tube and two pairs of inner electrodes made of a high resistance material and located in positions corresponding to the outer electrodes. The color switching is effected by applying switching signals to the two pairs of outer electrodes in opposite phase relationship.

Background of invention This invention is directed to improvements in o1' relating to a color picture tube of the type that an electron beam is deflected by using two electrostatic fields to alter its incidence angle to the grid to accomplish color switching. It has been well-known in the art that color switching is effected by deecting an electron beam with a magnetic field to change its incidence angle to the grid in a color tube and further, that an electron beam is electrostatically deected in a monochrome tube. However, the method utilizing a magnetic field requires larger power for this purpose and is attended by great unwanted radiation. This magnetic eld method can be employed for a line-sequential color television system but cannot be used for a dotsequential color television system. Therefore, it may be realized by those skilled in the art that color switching can be effected by conventional electrostatic deflection instead of using the magnetic eld. With this electrostatic deflection method, however, some problems are encountered in the provision of the power source for electrostatic eld generating electrodes and in shielding of the neck of the tube, because the neck is required to be longer than in the conventional cathode ray tube. In accordance with the present invention, inner electrodes and outer electrodes are provided on the inside and outside of the neck portion and they are electrostatically coupled and the outer electrodes are adapted to be grounded with respect to DC current, thereby solving the aforementioned problems.

Summary One object of this invention is to provide a one gun color picture tube in which electrodes are provided outside and inside of the neck portion and an electron beam is deected with low power for color switching.

Another object of this invention is to provide a one gun color picture tube of the type in which a one gun color demodulator circuit is simplified.

Still another object of this invention is to provide a one gun color picture tube which is adapted to minimize color distortion and unnecessary radiation, and hence is stable in operation.

Other objects, features and advantages of this invention will become apparent from the following descriptions taken in conjunction with the accompanying sheets of drawings.

Brief description of drawing FIGURE 1 is a connection diagram illustrating one example of a cathode ray tube of this invention as applied to a color television picture tube;

FIGURE 2 is a cross-sectional view of the part of the cathode ray tube;

FIGURE 3 is a cross-sectional view taken along the line A-A in FIGURE 2;

FIGURE 4 is an electrical equivalent circuit diagram of the principal part shown in FIGURE 2; and

FIGURE 5 is a curve representative of a color switching signal.

principal Description of preferred embodiment In FIGURE 1 reference numeral 1 indicates an antenna and 2 a color signal transmission system from which are obtained a luminance signal Y,l a chrominance signal Ss demodulated from a subcarrier, and horizontal and vertical synchronizing pulses PH and PV. Reference numeral 3 identifies generally a color cathode ray tube, which is designed so that its electron gun 4 is supplied with a low-frequency component YL of, for instance, 0 to 2 mc. of the luminance signal Y through an amplifier 5, a high-frequency component YH of 2 to 4 mc. of the luminance signal Y and the chrominance signal CS through an amplifier 6. The chrominance signal Cs is fed to a color burst signal separator 7. To the color burst signal separator 7 is applied one portion of the output from a horizontal deflection circuit 8 having fed thereto the horizontal synchronizing signal PH, selecting a color burst signal. The output of the color burst signal separator 7 is fed to a color switching signal generator 15, from which is obtained a sinusoidal signal fs of 3.58 mc. and applied to outer electrodes 9b and 10a of the cathode ray tube 3. Further, one portion of the sinusoidal signal f5 is fed to a multiplier 11, from which a sinusoidal signal 2f, of 7.16 mc. is applied to outer electrodes 9a and 10b. In addition, one portion of the sinusoidal signal fs of 3.58 mc. is fed to a key-out signal generator 12, from which a key-out signal of 10.7 mc. is applied to the electron gun 4 after being superposed on the: low-frequency component YL transmitted from the amplifier 5. Further, a deflection yoke 14 is supplied with the outputs of the horizontal deflection circuit 8` and a vertical output circuit 13.

The color cathode ray tube 3 includes a color phosphor screen 16 composed of red, green and blue phosphor strips R, G and B extending vertically of the face of the tube, and sequentially arranged in a repeating cyclic order which may be, for example, red, green, blue and red. Adjacent the color phosphor screen there is provided within the tube a color selection grid 17 composed of many grid wires 17a, the grid wires being disposed opposite the lines of demarcation between the green and blue phosphor strips G and B, and running parallel to the lengths of the phosphor strips. An electron beam 18v emanating from the electron gun 4 is caused to always impinge upon the red phosphor strips R, and the color selection grid 17 is supplied with a potential lower than that applied to the color phosphor screen. In addition, the inner surface of a conical portion 3a is coated with a highvoltage conductive layer 19, to which a high potential is applied.

In accordance with the present invention, two pairs of electrodes 9a, 9b and 10a, 10b are mounted on a neck portion of the tube rearwardly and forwardly of the detiection yoke 14. The electrodes of each pair are oppositely disposed in a direction perpendicular to the longitudinal direction of the phosphor strips. These electrodes may be disposed in close proximity of the deflection yoke 14 or may partly underlie it, and they are formed by vapor deposition or coating of, for instance, a conductive material. Furthermore, it is preferred that the electrodes located forwardly of the deection yoke 14 partly extend over the conical portion of the tube. High resistance layers 20 having a resistance value described later are provided on the inner surface of the neck portion at those locations corresponding to the electrodes 9a, 9b and 10a, 10b. One end of each high resistance layer 20 is grounded with respect to AC current, as will be hereinafter explained. It is desirable that the area of each high resistance layer 20 is greater than that corresponding to each of the electrodes 9a, 9b and 10a, 10b. In the illustrated example, the high resistance layers 20 are formed on the inner surfaces of the conical portion 3a and the neck portion 3b between the high-voltage conductive layer 19 and the electron gun 4. Further, grooves 21 are formed in the high resistance layers 20 in parallel to the tube axis for applying a high voltage to the electron gun 4 from the high-voltage conductive layer 19. In each groove 21 a conductor 22 is formed and its both ends are connected to the high-voltage conductive layer 19 and the electron gun 4 respectively. One end of each high resistance layer 20y is connected to the highvoltage conductive layer 19. It is preferred that the conductors 22 are each disposed at a location corresponding to the intermediate portion between the electrodes 9a and 9b. In addition, it is also preferred that an annular conductive zone 23 is provided at a place corresponding to the intermediate portion between the pairs of electrodes 9a, 9b and 10a, 10b.

Color switching signals are applied to the outer electrodes 9a, 9b and 10a, 10b. To this end, the output of the color switching signal generator 15 is connected between the electrode 9b and the ground, while the output of the multiplier 11 for producing the signal ZS, namely the circuit for forming the signal 215 is connected between the other electrode 9a and the ground. Similarly, the output side of the color switching signal generator 15 and that of the multiplier 11 are connected respectively to the other pair of electrodes a and 10b, but the connections are in opposite relation to the electrodes 9a and 9b. That is, the relationship is such that when the output end of the circuit is connected to the electrode 9b it is connected to the electrode 10a. lFurther, a shield plate 24 is disposed on the outside of the outer electrodes 9a, 9b and 10a, 10b through an insulating layer.

In the color cathode ray tube described above, electrostatic capacitances as identiied at 25a and 25b in FIG- URE 4 are established between the electrodes 9a, 9b and the high resistance layers opposite thereto, and an electrostatic capacitance as indicated by 26 is also yielded between the confronting portions of the layers 20 inside of the neck portion, since the layers 20 have a considerably high resistance value. These capacitances a, 25b and 26 are equivalently such as connected in series to one another, as illustrated in FIGURE 4. Moreover, since the end of each of the high resistance layers 20 is grounded with respect to AC current, the connecting points between the capacitances 25a, 25b and 26 are grounded through resistance elements or leakage resistances 27 of the high resistance layers, thence through capacitance `40 and to the ground connection 42. -In this manner, although a high DC potential may be maintained on the high resistance layers 20, any iniluence of AC current is eliminated by the grounding of these layers 20 through the capacitance `40r to ground connection 42. Reference numerals 28a, 28b, 29a and 29b designate capacitances established between the electrodes 9a, 9b, 10a and 10b and the shield plate 24. This implies that the color switching signal generator 15 is connected between one end 30b of the series capacitances and the ground and that the multiplier 11 is connected between the other end 30a and the ground. This grounding is accomplished through the secondary windings 15a and 11a of the color switching generator 15 and multiplier 11, respectively. One side of each of these secondaries 15a and 11a is directly connected to ground by ground connections 15b and 11b as shown. By these grounding connections it is assured that any DC potential on electrodes 9a and 9b, 10a and 10b is eiectively grounded and only the AC color switching signals fs and 2fs are applied to the electrodes. In this case, the output sides of the circuits 15 and 11 and the capacitances 28th and 28a respectively connected in parallel thereto are adapted to perform parallel resonance with respect to the signals fs and 2fs respectively.

The resistance value of the high resistance layers 20y is selected such that the time constant dependent upon the resistance value of the leakage resistances 27 and the capacitance value of the capacitance 25a or 25b is sufciently greater than the period of the color switching signal fs. Since the distance between the electrodes of the capacitance 25a or 25b is shorter than that of the capacitance 26 and the dielectric constant between the electrodes is greater than that of the capacitance 26, the capacitance value of the capacitance 25a or 25b is remarkedly greater than that of the capacitance 26. Accordingly, the signal fs is applied between the terminals 30a and 30b, namely between the electrodes 9a and 9b, and almost all of its signal voltage is concentrated on the capacitance 26. That is, an electrostatic field of the signal fs is produced in the neck portion 3b corresponding to the portion between the electrodes 9a and 9b. In a similar manner, an electrostatic iield of the signal 295 is yielded in the tube. These electrostatic -elds are composed to produce such a color switching electrostatic iield 31 as shown in FIGURE 5, which varies with the lapse of time.

Similarly, a color switching electrostatic flield 32 is yielded in the tube at a location corresponding to the electrodes 10a and 10b. This electrostatic field 32 is opposite in phase to that established by the electrodes 9a and 9b. In FIGURE 4 reference numerals 33a and 33b indicate capacitances established by the electrodes 10a and 10b and the high resistance layers 20. Reference numeral 34 designates a capacitance produced between the high resistance layers 20 disposed opposite to the electrodes 10a and 10b, and a leakage resistance 35 between these capacitances. As shown, the resistance 35 is also connected through capacitance 40' to ground connection 42, thereby effectively grounding the high resistance layers 20l corresponding to the location of electrodes 10a and 10b, with respect to AC current.

Since the electrostatic iields are produced in the tube as above described and the electron beam 18 is not deflected by the outer electrodes 9a, 9b and 10a, 10b at the zero portion 31R of the color switching signal 31, the electron beam is impinged upon the red phosphor strip R as described previously. In a similar manner, when the color switching signal approaches its negative peak value 31G the electrode 9b becomes negative, the electron beam 18 is diverged on the side of the electrode 9a and is then converged on the side of the electrode 10b, thereafter being impinged upon the green phosphor strip G adjacent the red phosphor strip R. When the color switching signal 31 approaches its positive peak value 31B, the electron beam 18 is diverged and is then converged in directions opposite to those in the foregoing, thereafter being impinged upon the green phosphor strip B. In this manner, the electron beam is electrostatically deected by the color switching signal and the color switching signal is synchronized with the chrominance signal fed to the electron gun 4, so that a color picture is reproduced 'on the color phosphor screen 16.

Where the capacitance values of the capacitances 25a and 25b are, for example, 100 pf. and the resistance value of the leak resistances 27 is 10 m9, their time constant is 1 milli-second. This time constant is suiciently greater than the period of the color switching signal when color reproduction is carried out in a dot-sequential manner. Accordingly, this invention is applicable not only to dot-sequential color reproduction but also to line-sequential color reproduction at a frequency of 5.25 kc. lower than 3.58 mc. Meanwhile, the resistance value of the high resistance layers 20 is selected such that charges stored on the inner wall of the tube by secondary electrons produced in the tube may be evolved through the layers 20. Therefore, when a beam current from the electron gun 4 is 300 ha. or so, if secondary electrons of 50 ua. which is about 1/6 of the current are emitted from the color selection grid 17 and some secondary electrons of 20 ua. which is about 1/2.5 of 50 ya. reach the high resistance layers 20, the secondary electrons flow to the ground through one of the leakage resistances 27 and thereafter to ground connection 42. A voltage drop in each leakage resistance 27 is such that when its resistance value is approximately m52,

lO/ta. X 10mi): 100 v.

This is fully smaller than the peak value (about 1.5 kv.p.p.) of the color switching signal 31, so that if the leakage resistance 27 has a value in the range of 1 to 10 mtl, a color switching electrostatic eld is established in the tube and the potential distribution in the tube is not disturbed. The high resistance layers 20 can be formed by vapor deposition of, for example, chrome oxide.

In the case where the peak value of the color switching signal is 1.5 kv.p.p. (which can be obtained by selecting the deflection angle at the neck portion to be about 128') and the capacitance values of the capacitances 25a and 25b are 50 pf., reactive power that a color switching signal of 3.58 mc. passes through the two capacitances 25a and 25h is approximately 315 w. Where the inductance of a coil connected to both ends of the series capacitances is about 40 Mh. and the coil is adapted to resonate with the color switching signal and its Q is about 120, the power of the color switching signal is 2.5 w. In practice, the value of the capacitances 25a and 25b can be made smaller, and hence the deflection power can also be decreased. However, since the capacitances 28a, 28b, 29a and 28b to the shield plate 24 are approximately 30 to 200 pf., the deflection power is selected inthe range of 3 to l0 w. in practice.

In a chromatron tube having a color grid disposed opposite to the color phosphor screen, the capacitance of the grid is about 2000 pf., a color switching signal is about 400 v.p.p., reactive power is approximately 2000 w. and deflection power is about 25 w. (in the case of Q=80). They are about four and ten times as great as those of the cathode ray tube of this invention. Further, it is considered that color switching is electromagnetically effected in the vicinity of the neck portion. In this case, the capacitance of the resonance circuit including the deflection is about 700 nf., the color switching signal is 700 v.p.p. or so, the reactive power is 1000 w. and the deflection power is approximately 1l w. (in the case of Q=90). They are about 3.5 and 4.5 times as great as those of the cathode ray tube of this invention. It will be seen from the foregoing that this invention requires an extremely low power for color switching. In addition, the construction of the color switching device is very simple, as will be seen from the drawings. Furthermore, the distance of the grid wires 17a of the color selection grid 17 corresponds to the -width of three phosphor strips and this distance is greater than that in the conventional chromatron tube. This invention does not necessitate connection of every other grid wire 17a and insulation of adjacent ones, and hence enables easy manufacture of the cathode ray tube. Moreover, the number of the phosphor strips constituting picture elements between adjacent grid wires 17a is great, so that a picture can be reproduced with high resolution.

The color switching frequency is as high as 3.58 mc., but the deflection power required is small as described above. This enables electron beom deflection with a relatively small power by such a color switching signal that the signal 215 of multiplied frequency is superposed on the signal fs, the period of the electron beam staying on each phosphor strip is lengthened as illustrated in FIGURE 5 and the period of the electron beam moving from one phosphor strip to adjacent one is shortened. Therefore, the use of such a color switching signal provides a color cathode ray tube which is free from color distortion and stable in operation. Further, in this case the signals f5 and 2fs can be applied separately between either one of the electrodes 9a and 9b and the ground, and when the capacitances 28a and 28b between the electrodes 9a and 9b and the shield plate 24 are each utilized as one element of the resonance circuit of the signal supply circuit, the shield plate 24 can be used as one element of the input circuit of the color switching circuit as well as serving to prevent the color switching signal from radiation to the outside. In such a case, it is considered possible to apply the signals fs and 2fs in series between either one of the electrodes and the ground, but in this case even if either one of the capacitances 28a and 28b is employed as one input circuit of the signal, another capacitance element is required as the other input circuit. In the cathode ray tube of this invention, however, such a capacitance element is not required.

It is considered that, for accomplishing color switching electrostatically, a color switching deflection plate is disposed in the cathode ray tube in the same manner as an electrostatic deflection plate in a usual electrostatic deflection type cathode ray tube. In this case, however, a tube and the same high potential as that applied to the high-voltage conductive layer 19 must be fed to the color switching deflection plate so as to ensure that the potential of the electron beam path is not disturbed by the insertion of the color switching deflection plate. Therefore, attention must be paid to insulation of the lead for deilection AC voltage application and for high voltage application. This makes it diflicult to provide the deflection yoke in position and the insertion of the color switching deflection plate is impossible. In the cathode ray tube of the present invention, however, the electrodes 9a, 9b and 10a, 10b are supplied with only the color switching signal and are grounded with respect to DC current, so that such a difficult insulation as mentioned above is not required. Further, with only the electrodes 9a, 9b and 10a, 10b provided on the outside of the tube, there is caused such an adverse influence that the inner surface of the neck portion 3b is charged with secondary electrons as above described to change the potential of the electron beam path, deteriorating focusing of the electron beam. In order to avoid this, the high-voltage conductive layer 19 is extended on the inner surface of the neck portion 3b at places corresponding to the electrodes 9a, 9b and 10a, 10b. The high-voltage conductive layer 19 is grounded with respect to AC current, so that no color switching field is produced. In the cathode ray tube of this invention the high resistance layers 20 are provided in the neck portion at places opposite to the electrodes 9a, 9b and 10a, 10b and their resistance value is selected as above described. As a result of this, a color switching field can be established in the tube without any trouble and the inner surface of the tube has a DC potential. That is, there is no possibility that the potential of the electron beam path varies to deteriorate focusing of the electron beam. Further, with the conductors 22 formed in the grooves 21 in the high resistance layers 20, a high voltage can be applied, with a low resistance, from the high-voltage conductive layer 19 through the conductors 22 to the electron gun 4.

In the foregoing, the signal 215 is superposed on the signal fs but color switching can be carried out by superposing a signal 3fs having a frequency which is three times as high as the signal fs. In some cases, color switching may be effected by the signal f5 only and in such a case the signal fs can be applied to the electrodes 9a and 9b in opposed phase.

It will be apparent that many modifications and variations may -be effected without departing from the scope of the novel concepts of this invention.

I claim:

1. In a cathode ray tube including an envelope having a color phosphor screen made up of arrays of different color phosphors and a conductive layer on a portion of the inner surface of said envelope leading to said screen, an electron gun for emitting an electron beam and a grid adjacent said screen and through which said beam can pass to impinge on said screen; electrostatic color switching means comprising irst and second pairs of electrodes disposed on the exterior of said envelope at locations between said gun and grid which are spaced in the general direction of said beam, the electrodes of each of said pairs being disposed in opposed relation, layers of high resistance material on the inner surface of said envelope only at locations substantially corresponding to those of said electrodes of each of said pairs, means to ground said high resistance layers as to alternating current, means connected between one of said electrodes of said 'lrst pair and ground and between the oppositely disposed electrode of said second pair and ground for applying a first AC deflection voltage to the electrodes connected thereto, and means connected between the other of said electrodes of said rst pair and ground and between the electrodes of said second pair which is disposed oppositely thereto and ground for applying a second AC deflection voltage to the respective electrodes, whereby to establish an electrostatic dellection eld for changing the angle of incidence of said beam at said grid in accordance with said irst and second AC deflection voltages.

2. A cathode ray tube as described in claim 1 wherein said first and second AC deection voltages are in opposed relation with respect to each other.

3. A cathode ray tube as described in claim 1 wherein said irst and second pairs of electrodes disposed on the exterior of said envelope are grounded with respect to DC current.

References Cited UNITED STATES PATENTS 2,672,575 3/ 1954 Werenfels 315--21 2,685,660 8/1954 Norgaard. 2,803,781 8/1957 Jurgens 315-21 X 2,923,846 2/ 1960 Partin 315-21 X RODNEY D. BENNETT, Primary Examiner B. L. RIBANDO, Assistant Examiner 

